Abstract: The causes of a liner parts fracture were analyzed by means of macroscopic observation, metallographic examination, scanning electron microscope analysis and hardness test. The results show that after local quenching treatment, the microstructure of the liner end became abnormal coarse martensite, the hardness increased and the brittleness increased. The liner was subjected to friction and extrusion during use, and brittle fracture occured when the pressure reached a certain degree.